Method for recovering rhodium from reaction products of oxosynthesis

ABSTRACT

The invention relates to a method for separating and recovering rhodium from reaction products of oxosynthesis, especially reaction products containing cobalt. The invention also relates to the reuse of rhodium as a catalyst for hydroformulation and to a catalyst for hydroformulation itself. The inventive method is characterized by the following: extraction of the organic solution with an aqueous phosphate solution or a phosphate solution, water washing, oxidative treatment of the organic phase, and extraction of the organic phase with an aqueous water-soluble arylphosphine solution.

This application is a 371 of PCT/EP01/00759 filed Jan. 24, 2001.

The present invention relates to an improved process for removing andrecovering rhodium from oxo process reaction products.

The preparation of aldehydes and alcohols by addition of carbon monoxideand hydrogen to olefinic double bonds (hydroformylation) is well known.The reaction is catalyzed by metals or compounds thereof of the 8^(th)transition group of the Periodic Table which form carbonyl orhydridocarbonyls under the reaction conditions. While cobalt and cobaltcompounds used to be used as catalysts, rhodium catalysts are todayfinding use to an increasing extent, even though rhodium is severaltimes more expensive than cobalt. Rhodium is used alone or incombination with complexing agents, for example organic phosphines.While the oxo process requires reaction pressures of from 25 to 30 MPausing rhodium as catalyst, pressures of from 1 to 5 MPa suffice whenrhodium complexes are used.

In many cases, rhodium catalysts have distinct advantages. They havehigher activity and selectivity and additionally facilitateuncomplicated operation of the production plants, in particular relatingto conduct of the synthesis and the excavation of the products from thereactor. Finally, the classic oxo process based on cobalt catalysts maybe converted in many cases to rhodium catalysts using the availableapparatus parts with only minimal capital expenditure.

Despite the advantages mentioned of the rhodium-catalyzed oxo process,the classic cobalt process continues to be operated in existing oldplants, in particular when conversion of the process to the rhodiummethod under the given economic conditions does not appear necessary.

Particular significance attaches to the recovery of rhodium which, afterthe reaction has ended, is present as the carbonyl compound dissolved inthe hydroformylation product. The work up comprises depressurizing thecrude oxo product in more than one stage by reducing the synthesis gaspressure from about 25 to 30 MPa initially to from 1.5 to 2.5 MPa. Thisreleases synthesis gas dissolved in the crude product. The mixture canthen be depressurized to atmospheric pressure. Before purification orfurther processing of the reaction product, by distillation, thedissolved rhodium compounds have to be removed. It has to be taken intoaccount here that only a few ppm of the noble metal are presenthomogeneously dissolved in the crude product. Also, in the course of thedepressurization procedure, rhodium can be converted to a metallic formor form multinuclear carbonyl compounds which separate from the liquidorganic phase as solids.

In the process known from EP-A-147824, rhodium is removed and recoveredby extracting it from the crude oxo product by means of complexingreagents.

The crude oxo product is the oxo process reaction mixture obtained afterdepressurizing and possible cooling.

In the known process, the complexing agents used are sulfonated orcarboxylated organic phosphines, preferably sulfonated arylphosphines.The sulfonated or carboxylated organic phosphines form water-solublecomplexes with rhodium. Accordingly, the rhodium may be extracted fromthe crude organic product using an aqueous solution of the substitutedphosphine.

This transfers the rhodium to the aqueous phase which can be removed bysimple decanting from the organic product mixture. Circulation of thecomplexing agent solution provides high rhodium concentrations in theaqueous phase.

According to EP-A-156253, the process disclosed by EP-A-0147824 isimproved by adding a solubilizer to the aqueous solution of thecomplexing agent. Its effect is in particular to alter the physicalproperties of the surface area between the two liquid phases and therebyto accelerate the transfer of the aqueous extractants into the productphase and that of the rhodium from the product phase into the aqueousphase. However, the effectiveness of the process described depends onthe quantity of solubilizer added. Its quantity cannot be increasedwithout limitation because the materials added unnecessarily burden theaqueous solution of the extractant and compromise its stability.

In the process disclosed by EP-B1-0 183 200, the depressurized crude oxoproduct is likewise extracted using an aqueous solution of a complexingagent. However, this process does not operate with the addition of asolubilizer, but instead employs sulfonated arylphosphines havingquaternary ammonium counter ions, for example thebenzyltrimethylammonium cation, as water-soluble complexing agents.

The prior art processes employ a catalyst solution which results fromhydroformylation reactions with rhodium catalysis.

However, problems occur where a hydroformylation plant initiallyoperated under cobalt catalysis is to be converted to rhodium catalysis.

For instance, EP-B1-0 111 257 concerns a hydroformylation process whichcomprises reacting the off gas from a first hydroformylation step (whichreacts olefin with carbon monoxide and hydrogen in the presence of acatalyst solution comprising an aqueous rhodium complex at low pressure)in a second step by the classical oxo process at high pressure and inthe presence of cobalt catalysts.

The conversion of this process to the complete rhodium method, i.e. alsocarrying out the/second step under rhodium catalysis, is the subjectmatter of EP-A1-0 805 138.

The organic phase resulting from conversion to the rhodium methodaccordingly comprises both rhodium and cobalt as catalytically activemetal.

Since rhodium is a precious metal, there is accordingly great interestin its removal, recovery and reuse as active catalyst metal from thecobalt-containing catalyst solution for economic reasons. It is ofdecisive importance that the rhodium occurs virtually completely in aform which allows reuse as a catalyst component. In order to obtainhighly optimal activity and selectivity for the recovered catalyst,virtually complete removal of the cobalt from the rhodium is sought. Itshould likewise be possible to recover rhodium virtually completelywhile at the same time retaining the activity and selectivity of thecatalyst solution after complete removal of the cobalt from thehydroformylation process or from the oxo process reaction products whichwere hitherto obtained by exclusive rhodium catalysis.

It is accordingly an object of the present invention to provide aprocess by which rhodium may be virtually completely recovered from anorganic catalyst solution in a simple manner. The catalyst solution mayadditionally comprise cobalt-containing compounds as impurities. At thesame time, it shall be ensured that rhodium is obtained in a formsuitable for reuse as catalyst. The rhodium compounds obtained shall besuitable for reuse both in a homogeneous hydroformylation processcarried out in the organic phase and also in the biphasichydroformylation process in the presence of water disclosed by DE-C-2627 354.

This object is achieved by a process for recovering rhodium from organicsolutions comprising rhodium complexes with or without cobalt complexesand with or without complexing ligands, which comprises

extracting the organic phase with an aqueous solution of a phosphate ofthe formula (O)P(OR¹)(OR²)(OR³), where R¹, R² and R³ are identical ordifferent and are hydrogen, a straight-chain or branched alkyl radicalhaving 1-10 carbon atoms or a substituted or unsubstituted aryl radicalhaving 6-10 carbon atoms, and the aryl radical is substituted bystraight-chain or branched alkyl radicals having 1-4 carbon atoms, orwith a phosphonate of the formula R⁴P(O)(OR⁵)(OR⁶), where R⁴, R⁵ and R⁶are identical or different and are hydrogen, a straight-chain orbranched alkyl radical having 1-10 carbon atoms or a substituted orunsubstituted aryl radical having 6-10 carbon atoms, and the arylradical is substituted by straight-chain or branched alkyl radicalshaving 1-4 carbon atoms;

washing the organic phase with water at a pH of from 0 to 8;

treating the organic phase after phase separation with an oxidizingagent at a temperature of from 0 to 100° C.;

treating the organic phase with an aqueous solution of a water-solublearylphosphine at elevated temperature and elevated pressure;

and removing the rhodium-containing aqueous solution from the organicphase by phase separation.

The procedure according to the invention is generally suited torecovering rhodium from an organic phase. An example of such an organicphase is the crude oxo product which is the reaction mixture resultingfrom the hydroformylation reaction after depressurization and optionalcooling, or the distillation residue of the crude oxo product afterremoving the aldehyde. Additionally, the organic phase may possibly alsocomprise cobalt compounds and/or complexing ligands, which is the casewhen a hydroformylation process hitherto carried out under cobaltcatalysis has been converted to the rhodium method. However, the processaccording to the invention may also be applied to rhodium recovery whenthe cobalt quantity originally present has been discharged in themeantime or the hydroformylation process has always been operated underrhodium catalysis.

The organic phase introduced into the recovery process comprises, inaddition to the desired aldehydes, condensation products thereof andalso alcohols. Complex ligands may also possibly be present, dependingon whether the old cobalt process was carried out in the presence of acomplexing ligand and whether the rhodium process is carried out usingcomplexing ligands. However, it is also possible to add complexingligands to the organic phase resulting from the hydroformylationreaction before further work up to stabilize rhodium complexes. Thecomplex ligands present are customary ligands in hydroformylationprocesses such as alkyl phosphines, alkylarylphosphines orarylphosphines, for example triphenylphosphine. Further componentspresent may include oxides derived from the complexing ligands, forexample triphenylphosphine oxide, which are dissolved in the organicphase.

The operation explained in the following describe the work up of arhodium-containing catalyst solution which additionally comprises cobaltcompounds as impurities. It will be appreciated that the procedureaccording to the invention can also be applied to those catalystsolutions comprising organic rhodium from which the cobalt has alreadybeen completely removed or which come from a hydroformylation processcarried out in the organic phase under rhodium catalysis.

As well as cobalt, rhodium is present at a concentration of from 10 to10 000 ppm, in particular from 100 to 5 000, preferably from 200 to 1000 ppm by weight, based on the total mass of the solution. The cobaltcontent is generally from 10 to 5 000 ppm by weight, based on the totalmass of the solution. In the further course of the hydroformylationprocess carried out under rhodium catalysis, the cobalt content fallsowing to the continuous discharge from the hydroformylation process. Theorganic phase comprises from 1 to 20, in particular from 1 to 10,preferably from 2 to 6% by weight of complexing ligands, based on thetotal mass of the organic phase. In addition, there are also oxidationproducts of the complexing ligands, such as phosphine oxides. Theconcentration is generally from 1 to 10% by weight, based on the totalmass of the organic phase. The organic components present includealdehydes, alcohols, aldols, condensation products and possibly olefin,if an olefin having at least 4 carbon atoms had been used for thehydroformylation reaction. Their relative quantity ratios depend onwhether the crude oxo product or the distillation residue obtainedtherefrom is selected for the work up process according to theinvention.

With the aid of the process according to the invention, it is possibleto remove rhodium which is generally present in low concentration withsurprisingly high selectivity and yield from the cobalt present inexcess.

In the process according to the invention, cobalt is first removed fromthe organic phase present.

To this end, the organic phase is extracted with an aqueous solution ofa phosphate of the formula (O)P(OR¹)(OR²)(OR³). R¹, R² and R³ areidentical or different and are hydrogen, a straight-chain or branchedalkyl radical having 1-10 carbon atoms, preferably 1-5 carbon atoms, ora substituted or unsubstituted aryl radical having 6-10 carbon atoms.The aryl radical may be substituted by straight-chain or branched alkylradicals having 1-4 carbon atoms. Preference is given to using anaqueous phosphoric acid solution or an aqueous solution of trimethylphosphate for extraction.

Aqueous phosphonate solutions can also be used in the extract step.Useful phosphonic acids include compounds of the formulaR⁴P(O)(OR⁵)(OR⁶). R⁴, R⁵ and R⁶ are identical or different and arehydrogen, a straight-chain or branched alkyl radical having 1-10 carbonatoms, preferably 1-5 carbon atoms, or a substituted or unsubstitutedaryl radical having 6-10 carbon atoms. If the aryl radical issubstituted, it carries straight-chain or branched alkyl radicals having1-4 carbon atoms. Preference is given to using an aqueous phosphonicacid solution where R⁴ is methyl, ethyl, propyl or butyl or an aqueoussolution of methyl dimethylphosphonate for extraction.

The concentration of the extractant in the aqueous solution is variableover a wide range. In general, aqueous solutions are used where theconcentration of the phosporos-containing extractants is from 1 to 95,preferably from 30 to 60% by weight, based on the aqueous extractionsolution.

When the extraction of cobalt is carried out at atmospheric pressure,operation is effected at a temperature of from 0 to 100° C., preferably20 to 40° C. However, it is also possible to treat the organic phasewith aqueous extractants under pressure at temperatures of from 100 to200° C., preferably from 120 to 140° C. When operation is effected attemperatures above 100° C., the pressure is generally from 0.5 to 20MPa.

In order to achieve sufficient phase separation, the volume ratio oforganic phase to aqueous extraction phase ranges from 20:80 to 80:20,preferably from 40:60 to 60:40. The extraction is generally carried outover a duration of from 0.5 to 5 hours, preferably from 1 to 3 hours.

The extraction step is generally repeated more than once, and theorganic phase is generally extracted from 2 to 4 times in succession.

To remove remaining quantities of extractant, the treated organic phaseis admixed with water at a temperature of from 0 to 100° C., preferablyfrom 20 to 40° C. The water quantity is generally from about 25 to 50%of the volume of the organic phase present. Water washing is carried outat a pH in the range from 0-8, preferably 4-8. To adjust the washingwater to the desired pH, an aqueous solution of an alkaline substancehaving a concentration of from 3 to 20% by weight is generally added tothe washing water. Preference is given to using aqueous solutions ofalkali metal hydroxides, alkaline earth metal hydroxides, alkali metalcarbonates, alkaline earth metal carbonates, alkali metal hydrogencarbonates or alkaline earth metal hydrogen carbonates, in particularsodium hydroxide or potassium hydroxide.

To achieve complete phase separation, it is frequently advisable to addan organic solvent. Useful solvents include aliphatic hydrocarbonshaving from 6 to 12 carbon atoms, aromatic hydrocarbons having from 6 to12 carbon atoms, aldehydes or condensation products thereof. It isparticularly advisable to add exactly the aldehyde which was the targetproduct of the oxo process. The quantity of the organic solvent addedcorresponds to the quantity of the organic phase treated.

The extraction to be carried out according to the inventive process withsubsequent water washing and pH adjustment leads to a reduction of thecobalt content in the organic phase treated of more than 90%, based onthe cobalt quantity originally present.

The organic phase present after extraction and water washing is thensubjected to an oxidative treatment. The oxidation of the organic phaseis carried out at temperatures of from 0 to 100° C., in particular from30 to 60° C. and preferably from 50 to 60° C. Since the organic phasecomprises aldehydes which either stem from the oxo process or have beenadded to support phase/separation during water washing, carboxylic acidsare formed during the oxidation. The formation of the carboxylic acidsand further oxidation products from the organic components isexothermic. In order to avoid an uncontrolled oxidation reaction,countercurrent cooling of the oxidation reactor may be required. In thecourse of the oxidation, not only the complexing ligand present inexcess, but also the rhodium complex itself will be attacked, whichconverts the ligand to a form which is no longer suitable forcomplexation. The phosphine oxides arise from the phosphines generallyused as complexing ligands and the rhodium complex falls apart.

The oxidizing agent used is pure oxygen or oxygen-containing gasmixtures, in particular air. However, it is also possible to use otheroxidizing agents, such as hydrogen peroxide, hydrogen peroxide-formingcompounds, hypochlorite, chromates or permanganates.

The oxidation may be carried out either under atmospheric pressure, orelse under elevated pressure. Useful pressures are from 0.1 to 2.0, inparticular from 0.2 to 1 and in particular from 0.3 to 0.7 MPa.

The oxidation time is generally from 0.5 to 24 hours. The exactoxidation time depends on the content of the complexing ligand in theorganic phase and may be determined by simple preliminary experiments.The course of the oxidation reaction is determined by gas chromatographydetermination of the complexing ligand content. As soon as thecomplexing ligand has completely reacted to give the correspondingoxide, the oxidation reaction is ended.

In a proven embodiment, a suitable reactor, for example, a stirredreactor equipped with an inlet nozzle and frit attachment or a tubularreactor provided with a gas distributor plate, which may contain arandom packing, is charged with the organic phase and the oxygen oroxygen-containing gas mixture is passed upward through the organicphase.

The organic phase obtained after the oxidative treatment is thenextracted with an aqueous solution of a water-soluble complexing ligand.The water-soluble complexing ligands are generally phosphines of theformula

Ar¹, Ar² and Ar³ are each a phenyl or naphthyl group, Y¹, Y² and Y³ areeach a straight-chain or branched alkyl group having from 1 to 4 carbonatoms, an alkoxy group, a halogen atom, an OH, CN, NO₂ or R⁷R⁸N group,where R⁷ and R⁸ are each a straight-chain or branched alkyl group havingfrom 1 to 4 carbon atoms, X¹, X² and X³ are each a carboxylate (COO⁻)and/or sulfonate (SO₃ ⁻) radical, n₁, n₂ and n₃ are identical ordifferent numbers from 0 to 5, M is an alkali metal ion, the equivalentquantity of an alkaline earth metal or zinc ion or an ammonium orquaternary alkylammonium ion of the formula N(R⁹R¹⁰R¹¹R¹²)⁺, where R⁹,R¹⁰, R¹¹ and R¹² are each a straight-chain or branched alkyl grouphaving from 1 to 4 carbon atoms, and m₁, m₂ and m₃ are identical ordifferent integers from 0 to 3, and at least one number m₁, m₂ or m₃ isequal to or greater than 1.

The aqueous solution contains from 1 to 40, in particular from 10 to 20,preferably from 10 to 15% by weight of water-soluble complexing ligands,based on the aqueous solution.

The aqueous solution comprising the complexing ligands is used in such aquantity that the molar ratio of rhodium to phosporus III is from 1:1 to1:200, preferably 1:10 to 1:20. The concentration of water-solubleligands in the aqueous solution is chosen taking into account thedesired molar ratio of rhodium to phosphorus III and against thebackground that the organic and aqueous phases should be present in aquantity ratio suitable for phase separation. In general, the volumeratio of organic to aqueous phase is from 30:70 to 70:30.

The extraction of the rhodium from the organic into the aqueous phase iscarried out at elevated pressure and elevated temperature. In general,pressures of from 1 to 20 MPa, preferably from 1 to 10 MPa, inparticular from 2.5 to 5 MPa and at temperatures of from 20 to 200° C.,preferably from 50 to 150° C., in particular from 120 to 140° C. areemployed.

The extraction is carried out either under the autogenous pressure,under pressurization of an inert gas, for example, nitrogen or a noblegas, or under synthesis gas pressure. The extraction time is generallyfrom 0.5 to 5 hours.

It is particularly advantageous to carry out the extraction in thepresence of synthesis gas. The composition of the synthesis gas, i.e.the ratio of hydrogen to carbon monoxide, may vary within a wide range.In general, the molar ratio of hydrogen to carbon monoxide is from 1:10to 10:1. Mixtures which comprise hydrogen and carbon monoxide in a molarratio of 1:1 are particularly suitable.

The extraction with aqueous complexing ligand solution under synthesisgas conditions leads to water-soluble rhodium complexes which, as wellas the complexing ligands, also contain carbon monoxide and hydrogen incomplexed form. Catalytic activity is ascribed to such rhodium complexesand the aqueous catalyst solution obtained after phase separation may beused without further treatment for hydroformylating olefins by thebiphasic process, as disclosed, for example, by DE-C-26 27 354.

However, it is also possible to subject the aqueous rhodium-containingsolution obtained by the process according to the invention to a furtheroxidation after adding a water-soluble salt of a carboxylic acid havingfrom 7 to 22 carbon atoms in excess, based on rhodium, a processdisclosed, for example, by EP-B1-0 255 673 and EP-B1-0 367 957. Rhodiumcan be precipitated from this aqueous solution as a sparinglywater-soluble or insoluble compound, for example, in the form of rhodium2-ethylhexanonate, and be used in a hydroformylation process carried outmonophasically in the organic phase. Such a hydroformylation process isdisclosed, for example, by EP-B1-0 188 246.

As disclosed by EP-B1-0 255 673, useful oxidizing agents are preferablyoxygen or oxygen-containing gas mixtures, for example air. However, itis also possible to use other oxidizing agents, such as hydrogenperoxide, hydrogen peroxide-forming compounds, hypochlorite, chromatesor permanganates. The oxidative treatment leads to decomposition of therhodium complex containing the water-soluble ligands by the formation ofphosphorus (V) oxide compounds which are no longer capable of formingcomplexes from the water-soluble phosphines used in the extraction step.During the oxidation procedure, rhodium precipitates in the form ofwater-insoluble compounds, presumably as rhodium carboxylate. Theoxidation is carried out at a temperature of from 50 to 200° C. atatmospheric pressure or at elevated pressure of from 0.1 to 2.0 MPa overa period of from 0.5 to 24 hours. In an extension of the teaching ofEP-B1-0 255 673 and EP-B1-0 367 957, the aqueous solution is extractedafter the oxidation step using an organic solvent comprising an organicphosphine or diphosphine. The organic solvent used is an aliphatichydrocarbon having from 6 to 12 carbon atoms, an aromatic hydrocarbonhaving from 6 to 12 carbon atoms, preferably benzene, toluene or theisomeric xylenes, ethers, for example, diethyl ether, dibutyl ether, oralcohols, for example, butanol, the isomeric pentanols, ethylene glycolor diethylene glycol. The phosphines or diphosphines used may be, forexample, triphenylphosphine, tributylphosphine, tripropylphosphine,triethylphosphine, trioctylphosphine, diethylphenyl-phosphine,diphenylethylphosphine, diphenyl-(dimethylamino)phenyl-phosphine,methylcyclohexylanisylphosphine,2,2′-bis((diphenylphosphino)methyl)-1,1′-biphenyl,1,2-bis(diphenylphosphino)ethane or2,2′-bis((diphenylphosphino)methyl)-1,1′-binaphthyl.

The extraction of this solution using phosphines or diphosphinesdissolved in an organic solvent allows rhodium to be transferredvirtually quantitatively from the aqueous into the organic phase.

The extraction of the rhodium from the aqueous into the organic phase iscarried out under elevated pressure and elevated temperature. Ingeneral, pressures of from 1 MPa to 20 MPa, preferably from 1 MPa to 10MPa, in particular from 2.5 MPa to 5 MPa and temperatures of from 20° C.to 200° C., preferably from 50° C. to 150° C., in particular from 120°C. to 140° C. are employed.

The extraction is carried out either under autogenous pressure, underpressurization of an inert gas, for example, nitrogen or a noble gas, orunder synthesis gas pressure. The extraction time is generally from 0.5to 5 hours.

It is particularly advantageous to carry out the extraction in thepresence of synthesis gas. The composition of the synthesis gas, i.e.the ratio of hydrogen to carbon monoxide, may vary within a wide range.In general, the molar ratio of hydrogen to carbon monoxide is from 1:10to 10:1. Mixtures which comprise hydrogen and carbon monoxide in a molarratio of 1:1 are particularly suitable.

The organic solution comprising the complexing ligands is used in such aquantity that the molar ratio of rhodium to phosporus III is from 1:1 to1:200, preferably 1:10 to 1:20. The concentration of ligands in theorganic solution is chosen taking into account the desired molar ratioof rhodium to phosphorus III and against the background that the organicand aqueous phases should be present in a quantity ratio suitable forphase separation. In general, the volume ratio of organic to aqueousphase is from 30:70 to 70:30.

The rhodium-containing organic solution obtained by this method can beused as the catalyst solution in the hydroformylation process carriedout homogeneously, as disclosed, for example, by EP-B1-0 188 246.

The process according to the invention can be used with great success toremove and recover rhodium from the products of hydroformylation ofterminal and internal olefins having more than 3 carbon atoms. Whenbranched olefin starting materials are used, the process according tothe invention is particularly suitable for removing rhodium from thereaction products which [lacuna] from the hydroformylation of i-heptene,diisobutylene, tri- and tetrapropylene or of C8-olefins commerciallyavailable under the description Dimersol. When unbranched olefins areused in the hydroformylation reaction, the work up process according tothe invention can be used with particular success with hydroformylationproducts of propylene, n-butene, n-pentene and n-hexene, although theabsolute rhodium concentrations are generally lower.

The process according to the invention can be used with great successwhen hydroformylation steps hitherto carried out under cobalt catalysisare converted to the rhodium method, a process disclosed by EP-0 805138, which is a further development of the process according to EP-0 111257.

The process according to the invention may enable more than 95% of therhodium originally present to be recovered. The cobalt content in theconcentrated rhodium solution obtained is less than 1%, based on the sumof the metals rhodium and cobalt.

It will be appreciated that the process according to the invention isnot restricted to the work up of solutions which, as well as rhodium,also contain cobalt compounds as impurities. It can also be used withcatalyst solutions which stem from a process carried out under exclusiverhodium catalysis.

The nonlimiting examples which follow illustrate the invention.

1^(ST) EXAMPLE Work Up of a Used Rhodium/Triphenylphosphine-ContainingSolution

1 000 g of a used catalyst solution having the following composition:55% by weight of n-butyraldehyde, 2% by weight of triphenylphosphineoxide, 6.3% by weight of triphenylphosphine, 36.2% by weight ofhigh-boilers (generally aldol condensation products of butyraldehyde)and 0.5% by weight of low-boilers (generally hydrocarbons having from 3to 7 carbon atoms) and comprising 699 mg of rhodium (6.79 mmol) and 234mg of cobalt (3.97 mmol) are diluted by mixing with 1 000 g of freshn-butyraldehyde in a 4 l three-necked flask and then extracted twicewith 100 g of 65% phosphoric acid for 30 minutes at 22° C. each time.The phases are separated under gentle stirring likewise within 30minutes. The organic phase is then washed twice with 50 g of deionizedwater each time which had been set using 3 ml of NaOH (10% strength) toa pH of 5.8. After subsequent phase separation, the remaining organicphase is transferred to a 4 l three-necked flask equipped with a fritattachment and frit filter and aerated with 150 l/h of air at 55° C.over 12 hours at 55° C. After the oxidation had ended, 1969 g of organicphase were obtained. The organic phase is transferred together with199.8 g of an aqueous solution of trisodium tri(m-sulfophenyl)phospine(TPPTS) (corresponds to 101.9 mmol of P III, Rh: P=1:15) into a 5 lsteel autoclave and stirred in intensively for 3 hours at 5 MPa of CO/H₂pressure at 125° C. The reaction mixture is then transferred to a 4 lthree-necked flask equipped with a lower outlet and lower aqueous phase(144.2 g) is removed from the upper organic phase (1979 g). The aqueousTPPTS solution contains 687.7 mg of rhodium, corresponding to 98.4% ofthe rhodium quantity originally present in the starting solution. Thecobalt content in the aqueous TPPTS solution was below the analyticaldetection limit.

2^(nd) EXAMPLE Hydroformylation of Propylene Using the Rh/TPPTS SolutionObtained in Example 1

The Rh/TPPTS solution (P:Rh=14:1) obtained according to example 1 isadjusted by adding fresh TPPTS to a P:Rh ratio of 100:1. The rhodiumcontent is 260 ppm. The solution is charged into a 0.2 l stainless steelautoclave. The 0.2 l stainless steel autoclave equipped with a stirreris charged with propylene and a CO/H₂ mixture consisting of equal volumefractions in such a quantity as 10 l/h (STP) of off gas may be withdrawnfrom the reactor [l/h (STP) means 1 liter of off gas under atmosphericconditions (20° C. and 1 at) per hour]. At the same time, 300 ml perhour of aqueous catalyst solution are circulated through the reactor.The hydroformylation is carried out semicontinuously over 8 hours. Theremaining reaction parameters and the results of the hydroformylationare given in table 1.

TABLE 1 Hydroformylation of propylene in the presence of a worked-upcatalyst solution Experiment duration [h] 8 Temperature [° C.] 122Pressure [bar] 50 Rh content [mg/kg] 260 P (III) content [mmol/kg] 263Ligand/Rh 100 C3 introduction rate [g/h] 40 Activity [mol ofaldehyde/mol of Rh · min] 15.08 Productivity [kg of aldehyde/l cat. sol.· h] 0.213 Conversion [%] 37 n/i ratio 93/7

3^(rd) EXAMPLE Comparative Hydroformylation Example

A freshly prepared TPPTS solution is installed with 260 ppm of rhodiumacetate in the 0.2 l stainless steel autoclave. The P:Rh ratio is 100:1.Otherwise, the hydroformylation reaction is carried out as in example 2.The remaining reaction parameters and the results of thehydroformylation are given in table 2.

TABLE 2 Hydroformylation of propylene in the presence of a freshcatalyst solution Experiment duration [h] 8 Temperature [° C.] 122Pressure [bar] 50 Rh content [mg/kg] 260 P (III) content [mmol/kg] 265Ligand/Rh 100 C3 introduction rate [g/h] 40 Activity [mol ofaldehyde/mol of Rh · min] 15.53 Productivity [kg of aldehyde/I cat. sol.· h] 0.216 Conversion [%] 38 n/i ratio 93/7

As comparison of tables 1 and 2 shows, the work up process according tothe invention delivers a catalyst solution (table 1) which has virtuallythe same activity, productivity and conversion numbers as a freshlyprepared catalyst solution using a fresh rhodium quantity (table 2).

What is claimed is:
 1. A process for recovering rhodium from organicsolutions which comprise rhodium complexes and cobalt complexes with orwithout complexing ligands, comprising extracting the organic solutionwith an aqueous solution of a phosphate of the formula(O)P(OR¹)(OR²)(OR³), wherein R¹, R² and R³ are individually selectedfrom the group consisting of hydrogen, alkyl of 1-10 carbon atoms and asubstituted or unsubstituted aryl of 6-10 carbon atoms, with the arylsubstituted by alkyl of 1-4 carbon atoms, or with a phosphonate of theformula R⁴P(O)(OR⁵)(OR⁶), where R⁴, R⁵ and R⁶ are individually hydrogen,alkyl of 1-10 carbon atoms and aryl of 6-10 carbon atoms unsubstitutedor substituted by alkyl of 1-4 carbon atoms, and the rhodium complexesremain in the organic phase; washing the organic phase with water at apH of 0 to 8; treating the organic phase after phase separation with anoxidizing agent at a temperature of 0 to 100° C.; treating the organicphase with an aqueous solution of a water-soluble arylphosphine atelevated temperature and elevated pressure; and removing therhodium-containing aqueous solution from the organic phase by phaseseparation.
 2. The process of claim 1, wherein the organic phase isextracted with the aqueous solution of the phosphate or phosphonate asdefined in claim 1 at atmospheric pressure and at a temperature of from0 to 100° C.
 3. The process of claim 1, wherein the organic phase isextracted with the aqueous solution of the phosphate or phosphonate asdefined in claim 1 at a pressure of from 0.5 to 20 MPa and at atemperature of from 100 to 200° C.
 4. The process of claim 1, whereinR¹, R², R³, R⁴, R⁵ and R⁶ are individually alkyl of 1 to 5 carbon atoms.5. The process of claim 1, wherein a phosphoric acid, trimethylphosphate or methyl dimethylphosphonate extractant is used.
 6. Theprocess of claim 1, wherein the water wash is effected at a pH of from 4to
 8. 7. The process of claim 1, wherein the organic phase is oxidizedwith a member selected from the group consisting of oxygen,oxygen-containing gas mixtures, hydrogen peroxide, hydrogenperoxide-forming compounds, hypochlorite, chromates and permanganates.8. The process of claim 1, wherein the oxidizing agent used is air. 9.The process of claim 1, wherein the oxidation is carried out at atemperature of from 30 to 60° C.
 10. The process of claim 1, wherein theoxidation is carried out at a pressure of from 0.1 to 2.0 MPa.
 11. Theprocess of claim 1, wherein the organic phase obtained after oxidativetreatment is extracted with an aqueous solution of a phosphine of theformula:

wherein Ar¹, Ar² and Ar³ are individually phenyl or naphthyl, Y¹, Y² andY³ are individually selected from the group consisting of alkyl of 1 to4 carbon atoms, alkoxy, halogen, OH, —CN, —NO₂ and R⁷R⁸N—, where R⁷ andR⁸ are individually alkyl of 1 to 4 carbon atoms, X¹, X² and X³ areindividually carboxylate (COO⁻) or sulfonate (SO₃ ⁻), n₁, n₂ and n₃ areindividually integers from 0 to 5, M is selected from the groupconsisting of an alkali metal ion, the equivalent quantity of analkaline earth metal, zinc ion, an ammonium and quaternary alkylammoniumion of the formula N(R⁹R¹⁰R¹¹R¹²)⁺, where R⁹, R¹⁰, R¹¹ and R¹² areindividually alkyl of 1 to 4 carbon atoms, and m₁, m₂ and m₃ areindividually integers from 0 to 3, and at least one of m₁, m₂ or m₃ isequal to or greater than
 1. 12. The process of claim 11, wherein theextraction is carried out at pressures of from 1 to 20 MPa, and attemperatures of from 20 to 200° C.
 13. The process of claim 10, whereinthe extraction is carried out in the presence of synthesis gas.